Heat treatment jig and heat treatment method for silicon wafer

ABSTRACT

In this heat treatment jig and method for silicon wafers, a silicon wafer is heat-treated while being mounted on support projections provided on three support arms, having an intervening spacing, protruding from a support frame towards the center. At that time, all the support projections under the silicon wafer are positioned on a same circle within a region where a radial distance from the center is defined by 85 to 99.5% of the wafer radius, and the support arms form an angle of 120° with each other about the center. With this jig and method, free depth of a dislocation generated from a pin position can be controlled deeper than a device formation region, and a widest slip-free region where the surface is free from slip dislocation is obtained.

TECHNICAL FIELD

The present invention relates to heat treatment jig for a wafer and heattreatment method for a wafer, specifically relates to a technologysuitably used in RTA or the like.

Priority is claimed on Japanese Patent Application No. 2003-097365 filed31 Mar., 2003, the content of which is incorporated herein by reference.

BACKGROUND ART

Conventionally, a rapid thermal annealer (RTA) is well known as a heattreatment apparatus for rapid heating and rapid cooling of a siliconwafer. As described in FIG. 3( a) of Patent Reference 1, a ring-shapedwafer holder 100 is mounted within a furnace of the rapid thermalannealer in order to maintain a horizontal orientation of the wafer.

As shown in Patent Reference 2, in another well known type of waferholder, a wafer is supported by a plurality of points.

However, in the heat treatment of wafers horizontally supported duringthe treatment, there has been a problem of yield reduction caused bygeneration of slip dislocations. It is considered that, since supportedportions of the wafer are pressed by their own weight, sliding frictionbetween the wafer and the projections is caused by warping of the waferduring the heat treatment or by a difference in heat expansion, strainoccurs in a portion of concentrated weight, and therefore each portionsupported by support projections generates slip dislocations.

In conventional wafer holders, reduction of slip dislocation is devised.An art of Patent Reference 2 is directed to reducing slip dislocationcaused by the presence of an orientation flat.

For reduction of slip dislocations in a wafer lacking an orientationflat, Non Patent Reference 1 describes that, regarding support positionsof the wafer by a wafer holder having a plurality of support points, thesupport points are preferably positioned at a region where a radialdistance from a center is defined by 80 to 85% of the wafer radius.

Patent Reference 1: Japanese Unexamined Patent Application, FirstPublication No. 2002-134593. Patent Reference 2: Japanese UnexaminedPatent Application, First Publication No. 2002-170865.

Non Patent Reference 1: Takeda, R. et al. J. Electrochem. Soc., Vol.144, No. 10, October (1997), pp. L280-L282.

However, even a wafer lacking an orientation flat generates slips whenthe wafer is mounted on a wafer holder of a rapid thermal apparatus andheated rapidly under a furnace temperature of not less than 1000° C.There is still further demand for a greater reduction of suchdislocations.

DISCLOSURE OF THE INVENTION

Based on the above considerations the invention aims to provide a heattreatment jig and heat treatment method for wafers, by which free depthof dislocation generated from the pin points is maintained deeper than adevice formation region, and a widest slip-free region is obtained onthe wafer surface.

A heat treatment method for a silicon wafer of the invention is a heattreatment method for a silicon wafer in a heat treatment furnace. Inthis method, the above described problem was overcome by supporting awafer at three support positions within a region where a radial distancefrom a center is defined by 85 to 99.5% of the wafer radius.

A heat treatment method for a silicon wafer of the invention is a heattreatment method using a three-points supporting device having: threesupport arms protruding from a support frame towards a center so as toform an intervening spacing with each other; and support projectionsprojecting upwards from each support arm, on which a silicon wafer ismounted and heat-treated in a heat treatment furnace.

When all the support projections are positioned around a same circleunder the wafer, all the support projections are positioned within aregion where a radial distance from the center is defined by 85 to 99.5%of the wafer radius, and the support arms are arranged so as to form anangle of 120° with each other about the center point. By this method,the above described problem was overcome.

A heat treatment jig of the invention is provided with a support frame;three support arms, protruding from the support frame towards the centerso as to form an intervening spacing with each other; and supportprojections projecting upwards from each support arm. The support armsare arranged so as to form an angle of 120° with each other about thecenter. Positions of all the support projections can be preset so thatthey are positioned around a same circle about the center point, withina region where a radial distance from the center is defined by 85 to99.5% of the wafer radius. With this jig, the above described problemwas solved.

In the invention, it is preferable that the support projections arefixed on the support arm so that the fixed position may be preset.

A wafer of the invention may be heat-treated by the above described heattreatment method for a wafer.

In a heat treatment method of the invention, by setting the supportpoints to form an angle of 120° about the center and to be positionedwithin a region where a radial distance from the center is defined by 85to 99.5% of the wafer radius, it is possible to control lengths of slipdislocations grown from the reverse surface of the wafer caused bycontact with the support projections, so that the dislocation lengthsare short enough not to affect a device formation region of the wafersurface.

By this method, generation of slip dislocations in the device formationregion is reduced and a reduction in wafer yield can be prevented.

When the support projections are positioned so that their radialdistances from the center are smaller than 85% of the wafer radius,contact defects occurring in the inner portion of the wafer being usedby device makers to manufacture a substrate cause a reduction in yields.In the case of a type having three support arms protruding from thesupport frame towards the center intervening spacing, elongated armlengths result in difficulties in maintaining a horizontal state, andafter being used for a long time, further difficulties in maintaining ahorizontal state are caused by the progression of arm deformation. Thisstate is not preferable, because an unbalanced in-plane load enlargesslips at a specific support projection. When the support projections arepositioned so that their radial distances from the center are greaterthan 99.5% of the wafer radius, in the wafer mounting process,unsatisfactory mounting of the wafer sometimes occurs because of a lackof margin. It is not preferable to support a wafer at its edge becauseslips generated at the edge easily cause cracking of the wafer.

When a center angle formed by the support projections on the samecircumference is set other than 120°, spacing angles of the supportprojections different from 120° cause an unbalanced load at eachprojection. A large load at a specific support point causes a longlength of slip dislocation occasionally penetrating the wafer to thesurface. When the supporting spacing is greater than 120°, there is apossibility that the wafer will drop in the direction of a large spacingbetween support positions. Therefore, this state is not preferable.

In the heat treatment jig of the invention, support projections areprovided on the upside of three support arms comprised of a first, asecond, and a third arm protruding towards a center intervening spacingfrom the support frame so that the arms forming an angle of 120° witheach other. The positions of the support projections can be preset sothat each projection is positioned in the same circle about the center,within a region where a radial distance from the center is defined by 85to 99.5% of the wafer radius. Accordingly, all the supporting positionsof a silicon wafer form an angle of 120° about the center and arepositioned within a region where a radial distance from the center isdefined by 85 to 99.5% of the wafer radius, thereby lengths of slipdislocations caused by contacts with support projections can becontrolled to sufficiently short lengths that do not affect the deviceformation region of the wafer surface.

In the invention, by enabling presetting of the fixing position of thesupport projection on the support arm and fixing the projection to thatposition, the support position of the wafer can be preset in accordancewith the diameter, thickness, hardness/stress properties, thermalproperties or the like of the wafer so that the length of slipdislocations caused by contact with the support projections can becontrolled to sufficiently short lengths that do not affect the deviceformation region of the surface of the silicon wafer.

As a practical construction, for example, it is possible to fit thesupport projections at fixing holes provided at predetermined positionson the support arms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an embodiment of a heat treatment jig for asilicon wafer of the invention.

FIG. 2 is an enlarged side view illustrating support arms shown in FIG.1

FIG. 3 is a schematic plan view of an embodiment of the heat treatmentmethod and heat treatment jig for a silicon wafer of the invention.

FIG. 4 is a sectional view of a heat treatment furnace.

FIG. 5 is a graph showing a relationship between the total slip lengthand the position of a support projection (pin position) of theinvention.

FIG. 6 is an image showing the condition of the wafer surface at the 70%support position in an example of the invention.

FIG. 7 is an image showing the surface condition of the wafer at the 97%support position in an example of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a heat treatment jig for a silicon wafer and a heattreatment method for a silicon wafer according to the invention isexplained below with reference to the drawings.

FIG. 1 is a plan view illustrating a heat treatment jig for a siliconwafer in the embodiment. A side view of a support arm in the embodimentis illustrated in FIG. 2. Positional relationships between the supportprojections and the silicon wafer in the embodiment are shown in aschematic plan view in FIG. 3.

In the drawings, numeral 1 indicates the heat treatment jig for asilicon wafer, and 10 indicates a support frame.

Firstly, this embodiment can be applied to a silicon wafer of 150 to 400mm in diameter, preferably 200 to 300 mm in diameter and lacking anorientation flat.

As shown in FIGS. 1 and 2, a heat treatment jig 1 of the embodiment has:a support frame 10 comprising approximately rectangular sides forming,in plan view, a rectangle-like shape one side of which is open; a firstsupport arm 31 provided at a side opposite to the opening of the supportframe 10; and a second and a third support arm 32, 33 provided at theother sides of the support frame 10.

Each of the first, second and third support arms 31, 32, 33 is formedintegrally with the support frame. The support frame 10, and supportarms 31, 32, 33 are formed from silica or SiC, or from SiC, a surface ofwhich is coated with polycrystalline silicon. Among these, silica is apreferable material because it is heat resistant and is impracticable asa source of contamination.

The support arms 31, 32, and 33 are placed in the same plane shared bythe support frame 10, and each arm protrudes from the support frame 10inwardly towards a center point C located at a near center position ofthe support frame 10. The support arms 31, 32, and 33 are provided so asto form an angle of 120° with each other about the center point C. Thatis, the second and the third support arms 32 and 33 are provided form,at their basal ends, an angle of 120° (60°) with sides of the supportframe 10.

Support projections 41, 42, and 43 are respectively provided to theupper sides of the support arms 31, 32, and 33. A position of eachsupport projections 41, 42, and 43 can be preset on the same circle C1about the center point C, and its outer radial position can be preset inthe region ranging from 85 to 99.5% of a radius R of a wafer W.

Here, the meaning of position of the support projections 41, 42, 43being in the region where a radial distance from the center is definedby 85 to 99.5% of the wafer radius is as follows. As shown in FIG. 3, ar/R×100(%) position is defined on a circle having a distance of r fromthe center C in the silicon wafer W of the radius R. When the r/R×100value varies within the above described range, the position defined by arange of r from a smaller r0 to a greater r1 corresponds to the abovedescribed position.

In the embodiment, as shown in FIG. 2, the support arms 31, 32 and 33are respectively provided with a plurality of fixing holes 51, 52, and53, to which the support projections 41, 42, and 43 are fitted, therebyenabling presetting of their fixing positions.

In the support arm 31, a plurality of fixing hole, 51, 51 is provided ata regular interval k. A similar constitution is applied for fixing holes52, 52 in the support arm 32, and fixing holes 53, 53 in the support arm33.

The support projection 41, 42, and 43 are formed from silica or SiC orfrom SiC a surface of which is coated with polycrystalline silicon.Among these, silica is a preferable material because it is heatresistant and is impracticable as a source of contamination.

The support projections 41, 42, and 43 are set to have positions on thesame circle C1 about the center point C, where, as shown in FIG. 3, theradius r of the circle C1 is in a region ranging from 85 to 99.5% of theradius R of the wafer W. At that time, a wafer W is mounted so as to beconcentric about the center point C.

The interval k of the respective fixing holes 51, 52, and 53 is set to avalue near 5% of the r/R value. The drawings also illustrate fixingholes at a position where a radial distance from the center is smallerthan 85% of the wafer radius. However, these holes are for a case suchas mounting a different size wafer W, and may be eliminated.

When the support projections are positioned so that their radialdistances from the center are smaller than 85% of the wafer radius, inthe inner portion of the wafer being used by device makers tomanufacture a substrate, the occurrence of contact defects causes areduction in the yield. In the case of a type having three support armsprotruding from support frame towards the center forming an interveningspacing with each other, elongated arm lengths results in difficultiesin maintaining of horizontal state, and after being used for a longtime, further difficulties in maintaining a horizontal state are causedby the progression of arm deformation. This state is not preferable,because an unbalanced in-plane load enlarges slips at a specific supportprojection. When the support projections are positioned so that theirradial distances from the center are greater than 99.5% of the waferradius, in the wafer mounting process, unsatisfactory mounting of thewafer sometimes occurs because of a lack of a margin. It is notpreferable to support a wafer at its edge because slips generated in theedge easily cause cracking of the wafer.

As shown in FIG. 3 a silicon wafer is mounted on the support projections41, 42, and 43 of the heat treatment jig 1 of the embodiment on whichthe support projections 41, 42, and 43 are positioned on the same circleabout the center point C of the wafer, thereby the wafer W is supportedhorizontally on the jig 1. After that, the heat treatment jig 1 for asilicon wafer is transferred into a heat-treatment furnace 20exemplified in FIG. 4 and the wafer is heat treated. By the abovearrangement of the silicon wafer on the heat treatment jig 1, it ispossible to reduce the generation of slip dislocation on the wafersurface during heat treatment. Numeral 21 in FIG. 4 indicates a heatinglamp, and 22 indicates a pyrometer.

Although a mono-layer type heat treatment furnace was used as the heattreatment furnace in the above embodiment, the invention can be appliedto a vertical heat treatment furnace capable of treating a plurality ofwafers arranged in a ladder boat or the like.

As a preset interval, fixing positions of the support projections mayhave a value different from 5% of the r/R value. The positions may beset at a non-regular interval.

EXAMPLE

An example of the invention is explained in the following.

Example 1

Silicon wafers lacking an orientation flat (notch-type silicon wafers)of 200 mm in diameter, 0.725 mm in thickness are prepared.

The support projections 41, 42, 43 shown in FIGS. 1 and 3 are positionedaround the same circle of radius r and are concentric with the wafer Wabout the center C. Where the wafer radius is termed R, the positionsare controlled so that the r/R value was varied at every 5% interval,from 65% to 90%, and was 97%. The silicon wafer W was mounted on thesupport projections with the above described arrangement and wassupported horizontally. The heat treatment jig 1 being mounted with thesilicon wafer was transferred to the heat treatment furnace 20 shown inFIG. 4, and the wafer W was heat-treated for 10 seconds at a furnacetemperature of 1250° C.

Comparative Evaluation

After the RTA treatment of the wafer supported by the reverse surface,the silicon wafer was etched with Secco etching liquid, and slipdislocations occurring on a surface as a device formation region wereobserved. When no dislocation has developed on the surface, an etch pitcannot be observed after the Secco etching. FIGS. 6 and 7 show theresults for r/R value of 70%, and 97% respectively.

In FIG. 6, where support projections (pin positions) are at 70%positions, lines on the image are drawn respectively for slips so thateach line is drawn between most remote dislocation. Then the length wasmeasured as the slip length.

Next, the cumulative length (sum) of the slip length was calculated foreach wafer. The results are shown in FIG. 5. The value is an averagevalue of results for the same support projection position (pin position)from a plurality of wafers.

Results

As shown in the results in FIG. 5, when the position of the supportprojection (pin position) is defined by a value greater than 85% of thewafer radius, the total slip length falls in a range of not more thanapproximately 7 mm, and production yield of wafers can be enhanced to alevel not actually affecting the device formation property.

In particular, as shown in FIG. 7, at a position defined by not lessthan 95%, preferably around 97%, slip dislocations do not appear on thewafer surface, and specifically well characterized wafers can beproduced.

INDUSTRIAL APPLICABILITY

By utilizing the heat treatment method and heat treatment jig forsilicon wafers of the invention, all the support positions of thesilicon wafer are arranged forming angles of 120° about the center, andare also arranged in a region where a radial distance from the center isdefined by 85 to 99.5% of the wafer radius. With this arrangement, thelength of slip dislocations caused by contact with the supportprojection can be suppressed so that the dislocation only grows to aregion not affecting the device formation region of the wafer surface.Accordingly, by reducing the generation of slip dislocation in thedevice formation region, a reduction of wafer yields can be effectivelyprevented.

1. A heat treatment method for heat treating a silicon wafer in atreatment furnace, comprising supporting a silicon wafer by threesupport positions within a region where a radial distance from a centeris defined by 85 to 99.5% of a wafer radius.
 2. A heat treatment methodfor a silicon wafer utilizing a three-points supporting devicecomprising: three support arms protruding from a support frame towards acenter so as to form an intervening spacing with each other; and supportprojections projecting upwards from each support arm, on which a siliconwafer is mounted and heat-treated in a heat treatment furnace, wherein,when all the support projections are positioned on a same circle, allthe support projections are positioned within a region where a radialdistance from the center is defined by 85 to 99.5% of the wafer radius,and the support arms are arranged so as to form an angle of 120° witheach other about the center point. 3.-4. (canceled)
 5. A wafer heattreated by the heat treatment method according to claim
 1. 6. A waferheat treated by the heat treatment method according to 2.